The present invention pertains to headlamp dimmers and components that can be used with a headlamp dimmer.
Modern automotive vehicles include a variety of different lamps to provide illumination under different operating conditions. Headlamps are typically controlled to alternately generate low beams and high beams. Low beams provide less illumination, and are used at night to illuminate the forward path when other vehicles are present. High beams output significantly more light, and are used to illuminate the vehicle""s forward path when other vehicles are not present. Daytime running lights have also begun to experience widespread acceptance.
Laws in various countries regulate vehicle illumination, and vehicle manufacturers must build cars that comply with these regulations. For example, regulations set forth by the United States Department of Transportation (DOT) regulate the light emissions of a vehicle""s high beam headlamps. Various state regulations are used to control the amount of glare experienced by drivers due to preceding vehicles (other vehicles traveling in the same direction) and oncoming vehicles (vehicles traveling in the opposite direction).
Known vehicle high beam headlamp emissions in accordance with the DOT regulations limit the intensity to 40,000 cd at 0xc2x0, 10,000 cd at 3xc2x0, 3250 cd at 6xc2x0, 1500 cd at 9xc2x0, and 750 cd at 12xc2x0. An example of an emission pattern meeting this regulation is illustrated in FIG. 1 of U.S. Pat. No. 5,837,994, entitled xe2x80x9cCONTROL SYSTEM TO AUTOMATICALLY DIM VEHICLE HEAD LAMPS,xe2x80x9d issued to Joseph S. Stam et al. on Nov. 17, 1998, the disclosure of which is incorporated herein by reference. In order to avoid an illuminance of 0.1 foot candles (fc) incident on another vehicle at these angles, the vehicle high beam headlamps should be dimmed within 700 feet of another vehicle if the vehicles are at an angle of 0xc2x0, within 350 feet of another vehicle if the vehicles are at a horizontal position of 3xc2x0, and 200 feet of the other vehicle if the position of the other vehicle is at an angle of 6xc2x0 to the longitudinal axis of the controlled vehicle. It can thus be seen that a preceding vehicle directly in front of the controlled vehicle (i.e., at an angle of 0xc2x0) will need to be identified well prior to the controlled vehicle catching up to the preceding vehicle, although the distance by which the controlled vehicle""s headlamps must be dimmed for a preceding vehicle can be somewhat less than for an oncoming vehicle because glare from behind is usually less disruptive than oncoming glare.
In order to automatically control the vehicle headlamps, various headlamp dimmer control systems have been proposed. In order to prevent drivers of other vehicles from being subjected to excessive glare levels, an automatic headlamp dimmer system must sense both the headlights of oncoming vehicles as well as the taillights of preceding vehicles. Some systems that effectively detect headlights are unable to adequately detect taillights. Most prior systems are unable to distinguish nuisance light sources, such as reflectors, street signs, streetlights, house lights, or the like, from light sources that require headlight control. Accordingly, these systems are subject to undesirable dimming of the high beams when no other traffic is present and turning on the high beams when other vehicles are present. In addition to the undesirable performance, it is difficult for prior systems to comply with the legal requirements as described above for high beam control while avoiding unnecessary dimming of the vehicle headlamps.
Fog lights are examples of other vehicle lights that are difficult to control automatically. Vehicles are known to include forward and rearward directed fog lights. In Europe, it is known to provide a very bright red or white light on the back of the vehicle which is illuminated under foggy conditions. The fog lights must be turned ON as soon as the fog reduces visibility by a predetermined amount and must turn OFF when the fog drops below that density. A reliable method of automatically controlling such fog lights has not been available.
Accordingly, there is a need for a more reliable and intelligent automatic lamp control for a vehicle.